Current Distribution of Armature Coils Combining Two Different Sizes of REBCO Racetrack Double Pancakes

We are currently developing superconducting electric propulsion armature coils which utilize REBa2Cu3Oy (REBCO) strands. To implement the REBCO coils in aircraft, the voltage must be reduced for safety concerns by using high-current capacity. Parallel conductors can be used to expand the current capacity, but the current cannot flow equally through each strand owing to the slight difference in inductance. We have investigated transposed parallel conductors which can almost equalize the inductance of each conductor. Conversely, the distributed windings for the armature coils can improve the magnetic field waveform and transform it into a sine wave by reducing the distortion of the magnetic flux density about the rotating magnetic field. However, it is difficult to implement a distributed armature winding using the REBCO strands since it is tape-shaped and difficult to twist. Therefore, we propose a distributed armature winding which combines two types of racetrack double pancakes. Each double pancake comprises two-strand insulated REBCO superconducting parallel conductors transposed inside the pancake for current equalization. In this study, we perform an experimental demonstration of the current equalization based on the transposition of the distributed armature winding. We made coils with two-strand as a simplified, but the actual coils were needed more 10 strand parallel conductors. In future works, we will manufacture transposed parallel conductor coils using much more strands and measure the current distribution. Additionally, this study measured the current distribution with only the stater. Thus, we will combine the rotor and measure the magnetic field distribution of the rotating magnetic field in the armature.

Automated summary

This study demonstrates the current equalization effect of the transposed distributed armature winding and proposes a distributed armature winding that combines two types of racetrack double pancakes. In future works, parallel conductor coils using more strands will be manufactured and the current distribution will be measured. Additionally, the magnetic field distribution of the rotating magnetic field in the armature will be measured by combining the rotor.